I'll tell you there are better builders on this site than I am. But building a bike from the frame up is a ton of fun, but it is not cheap. I did my first bike build in 1990. The most fun build was 3 years ago on '92 Serotta Mtb frame that needed a suspension fork with a 1" steerer. The fun is tracking everything down and getting a good final product. I can tell you every part, and probably where it came from without looking at the bike. Amped up enough?
But you do need to do your homework. Find a decent frame, not some discount store discard. A fork that is not worn out. The best route is to buy a good used bike and then learn to tear apart bearings and re-grease, swap out parts as needed. There are some gems out there, especially in the 26er world. You just have to be willing to adjust your budget, if you are able, to find a really good deal on a good bike. It dies not have to he expensive.
John